Large tanks (e.g., oil, water, or other fluid) often have a valve to release fluid from the tank when desired. These valves may fail (e.g., begin to leak) and need to be replaced. Before replacing the valve, the entire tank has to be drained to avoid spilling or otherwise losing fluid during removal and replacement of the valve. This can be time consuming and expensive, for example, if a tanker truck has to be brought in to temporarily store the fluid drained from the tank.